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2822 ADVANCED SUBSIDIARY GCE PHYSICS A Electrons and Photons FRIDAY 11 JANUARY 2008 Afternoon Time: 1 hour *CUP/T27964* Candidates answer on the question paper. Additional materials: Electronic calculator INSTRUCTIONS TO CANDIDATES • • • • • • • Write your name in capital letters, your Centre Number and Candidate Number in the boxes above. Use blue or black ink. Pencil may be used for graphs and diagrams only. Read each question carefully and make sure that you know what you have to do before starting your answer. Answer all the questions. Do not write in the bar codes. Do not write outside the box bordering each page. Write your answer to each question in the space provided. INFORMATION FOR CANDIDATES • • • • • FOR EXAMINER’S USE The number of marks for each question is given in brackets [ ] at the end of each question or part question. The total number of marks for this paper is 60. You will be awarded marks for the quality of written communication where this is indicated in the question. You may use an electronic calculator. You are advised to show all the steps in any calculations. Qu. Max. 1 8 2 9 3 9 4 7 5 12 6 15 TOTAL 60 Mark This document consists of 15 printed pages and 1 blank page. SP (SM/CGW) T27964/11 © OCR 2008 [T/100/3701] OCR is an exempt Charity [Turn over 2 Data speed of light in free space, c = 3.00 × 10 8 m s –1 permeability of free space, 0 = 4 × 10 –7 H m–1 permittivity of free space, 0 = 8.85 × 10 –12 F m–1 elementary charge, e = 1.60 × 10 –19 C the Planck constant, h = 6.63 × 10 –34 J s unified atomic mass constant, u = 1.66 × 10 –27 kg rest mass of electron, me = 9.11 × 10 –31 kg rest mass of proton, mp = 1.67 × 10 –27 kg molar gas constant, the Avogadro constant, R = 8.31 J K –1 mol –1 NA = 6.02 × 10 23 mol –1 gravitational constant, G = 6.67 × 10 –11 N m 2 kg –2 acceleration of free fall, g = 9.81 m s –2 © OCR 2008 3 Formulae uniformly accelerated motion, s = ut + 1 2 at 2 v 2 = u 2 + 2as 1 sin C refractive index, n= capacitors in series, 1 1 1 + +... = C C1 C2 capacitors in parallel, C = C1 + C2 + . . . capacitor discharge, x = x0e–t/CR pressure of an ideal gas, p= radioactive decay, x = x0e– λt 1 3 Nm 2 <c > V t = 0.693 λ critical density of matter in the Universe, relativity factor, 3H02 ρ0 = 8G = √ (1 – current, I = nAve nuclear radius, r = r0A1/3 sound intensity level, © OCR 2008 = 10 lg v2 ) c2 ( ) I I0 [Turn over 4 Answer all the questions. 1 A cell, a resistor of resistance 120 Ω and a negative temperature coefficient (NTC) thermistor are connected in series. (a) In the space below, sketch a circuit diagram of this arrangement. [2] (b) The cell has e.m.f. 1.4 V and negligible internal resistance. At a particular temperature, the current in the resistor is 5.0 × 10–3 A. (i) Calculate the potential difference across the resistor. potential difference = ……………………………. V [2] (ii) Calculate the resistance of the thermistor at this temperature. resistance = ……………………………. Ω [2] (c) State and explain how the potential difference across the resistor changes when the temperature of the thermistor is lower. ................................................................................................................................................... ................................................................................................................................................... ...............................................................................................................................................[2] [Total: 8] © OCR 2008 5 BLANK PAGE PLEASE DO NOT WRITE ON THIS PAGE © OCR 2008 [Turn over 6 2 (a) Draw a line from each of the named components on the left-hand side to the correct I-V characteristic on the right-hand side. I metallic wire at constant temperature 0 0 V I semiconductor diode 0 0 V I filament lamp 0 0 V [1] © OCR 2008 7 (b) In this question, two marks are available for the quality of written communication. Explain, in terms of resistance, the shape of the I-V graph for each component below. (i) Metallic wire at constant temperature. ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... (ii) Semiconductor diode. ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... (iii) Filament lamp. ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... [6] Quality of Written Communication [2] [Total: 9] © OCR 2008 [Turn over 8 3 (a) State one similarity between potential difference and electromotive force. ................................................................................................................................................... ...............................................................................................................................................[1] (b) Define the volt. ................................................................................................................................................... ...............................................................................................................................................[1] (c) (i) Define the kilowatt-hour (kW h). ........................................................................................................................................... .......................................................................................................................................[1] (ii) Determine the value of the kilowatt-hour in joules. 1 kW h = ……………………………… J [1] © OCR 2008 9 (d) A d.c. supply is connected across a variable resistor. The resistance of the variable resistor is changed. Fig. 3.1 shows the variation of the power P dissipated in the resistance R of the variable resistor. 5 P/W 4 3 2 1 0 0 2 4 6 8 R/Ω 10 12 Fig. 3.1 (i) Use Fig. 3.1 to determine the potential difference across the variable resistor when it dissipates maximum power. potential difference = ……………………………. V [3] (ii) Explain why your answer to (i) is not equal to the e.m.f. of the supply. ........................................................................................................................................... ........................................................................................................................................... .......................................................................................................................................[2] [Total: 9] © OCR 2008 [Turn over 10 4 Fig. 4.1 shows a section through a loudspeaker. cone N circular coil S S N magnet Fig. 4.1 The circular coil is free to move up and down in the space between the North and South poles of the magnet. The coil is connected to a d.c. supply of e.m.f. 1.5 V and of negligible internal resistance. (a) On Fig. 4.1, draw arrows to show the directions of the magnetic field between the poles of the magnet. [1] (b) The length of the wire in the coil is 24 m and its resistance is 8.0 Ω. The magnetic flux density of the magnetic field at the position of the coil is 1.2 × 10–2 T. Calculate the force experienced by the wire in the coil due to the magnetic field. force = ……………………………. unit ………. [4] (c) Wire of the same length and material but half the diameter of the original wire is used to make a similar coil. State and explain the change to your answer to (b) when this coil is used in place of the original one. ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ...............................................................................................................................................[2] [Total: 7] © OCR 2008 11 5 (a) State Ohm’s law. ................................................................................................................................................... ................................................................................................................................................... ...............................................................................................................................................[2] (b) From the list below, circle the quantity that is conserved in Kirchhoff’s second law. charge e.m.f. energy time [1] (c) Fig. 5.1 shows an electrical circuit. R E 2R Fig. 5.1 The battery has e.m.f. E and negligible internal resistance. The resistances of the resistors are R and 2R. Calculate (i) the total resistance of the circuit in terms of R resistance = ………………………[2] (ii) the current from the battery in terms of E and R. current = ……………………………..[1] © OCR 2008 [Turn over 12 (d) Fig. 5.2 shows a circuit. 12 Ω 0.16 A 0.48 A 18 Ω E 36 Ω I Fig. 5.2 The battery has negligible internal resistance. Determine (i) the charge passing through the battery in a time of 150 s charge = …………………………. C [2] (ii) the number of electrons responsible for the charge in (i) number = ……………………………[1] (iii) the current I in the 18 Ω resistor current = ………………….. A [1] © OCR 2008 13 (iv) the e.m.f. E of the battery. e.m.f. = ………………………………… V [2] [Total: 12] Please turn over for question 6. © OCR 2008 [Turn over 14 6 (a) State one main property of an electromagnetic wave. ................................................................................................................................................... ...............................................................................................................................................[1] (b) Arrange the following electromagnetic radiations in the order of increasing wavelengths. Start with the shortest wavelength. infrared visible light gamma rays microwaves ...............................................................................................................................................[1] (c) The table below shows the work function energies of some metals. metal (i) work function energy (eV) beryllium 5.0 magnesium 3.7 potassium 2.3 silver 4.7 zinc 4.3 Define the work function energy of a metal. ........................................................................................................................................... .......................................................................................................................................[1] (ii) State and explain which metal has the lowest threshold frequency. ........................................................................................................................................... ........................................................................................................................................... .......................................................................................................................................[2] © OCR 2008 15 (iii) A plate made of magnesium is illuminated with electromagnetic waves of wavelength 3.2 × 10–7 m. The electrons emitted from the surface of the plate have a range of kinetic energies. 1 Describe how the incident radiation interacts with the metal to release electrons from its surface and explain why these electrons are emitted with a range of kinetic energies. ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... .......................................................................................................................................[4] 2 Show that the maximum kinetic energy of the electrons emitted from the surface of the magnesium plate is 3.0 × 10–20 J. [3] 3 Calculate the de Broglie wavelength of an electron emitted with maximum kinetic energy. wavelength = ………………………….. m [3] [Total: 15] END OF QUESTION PAPER © OCR 2008 16 PLEASE DO NOT WRITE ON THIS PAGE Permission to reproduce items where third-party owned material protected by copyright is included has been sought and cleared where possible. Every reasonable effort has been made by the publisher (OCR) to trace copyright holders, but if any items requiring clearance have unwittingly been included, the publisher will be pleased to make amends at the earliest possible opportunity. OCR is part of the Cambridge Assessment Group. Cambridge Assessment is the brand name of University of Cambridge Local Examinations Syndicate (UCLES), which is itself a department of the University of Cambridge. © OCR 2008